Optical thread profiler

ABSTRACT

An apparatus configured to measure at least one physical characteristic of a threaded surface (e.g., an internally threaded surface) of an object is provided. The apparatus uses optical triangulation to perform non-contact characterization of the threaded surface. The apparatus can be used to characterize various aspects of the threaded surface, including generating the measurements required to produce a longitudinal cross-sectional profile of the threaded surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/962,922, filed Dec. 8, 2015, which is a continuation of U.S. patentapplication Ser. No. 14/474,067, filed Aug. 29, 2014, now U.S. Pat. No.9,234,748, which is a continuation of U.S. patent application Ser. No.13/493,806, filed Jun. 11, 2012, now U.S. Pat. No. 8,860,952, whichclaims the benefit of U.S. Provisional Application No. 61/495,083, filedJun. 9, 2011, the disclosures of which are incorporated herein byreference in their entirety.

BACKGROUND

Current technologies for measuring at least one physical characteristicof an internally threaded surface, such as the shape of a thread form,include the casting or rubber replicating process, such as byReporubber®, as illustrated in FIG. 14. The Reporubber® material isapplied over several threads, allowed to cure, and is then removed. Thematerial maintains its shape when removed. The resulting thread mold issliced on-axis and placed on an optical comparator, where it ismagnified. An overlay of the theoretical shape may be used to detectproblem areas. This is a time consuming process and relies on theoperator to perform the comparison, which can be subjective and requiresa “trained eye.”

Another current approach is to use a mechanical stylus to trace thethread form, such as with the use of a contour measuring system, asillustrated in FIG. 15. This method is time-consuming to setup andcollect data. It is also fragile.

Accordingly, there exists a need for improved internal threadmeasurement systems.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features ofthe claimed subject matter, nor is it intended to be used as an aid indetermining the scope of the claimed subject matter.

In one aspect, an apparatus configured to measure at least one physicalcharacteristic of an internally threaded surface of an object isprovided, wherein the internally threaded surface comprises a centralaxis of the object defined by a plurality of peaks of the internallythreaded surface in the longitudinal direction of the internallythreaded surface, and wherein the internally threaded surface has acylindrical latitudinal cross-section. In one embodiment, the apparatusincludes:

-   -   (1) at least one motion stage configured to controllably move an        optical head along a measurement axis of the internally threaded        surface, wherein the measurement axis and the central axis lie        in a common plane; and    -   (2) the optical head, comprising:    -   (i) an emission optical element in optical communication with a        first light source configured to emit a first incident light        beam onto the internally threaded surface to generate scattered        light off of the internally threaded surface at a measurement        point;    -   (ii) a detector optical element in optical communication with a        first detector configured to receive at least a portion of the        scattered light from the measurement point, wherein the detector        optical element has a receive axis defined by the measurement        point, the detector optical element, and the first detector, and        wherein the first detector is configured to output a detector        signal indicative of the intensity and position of the scattered        light on the detector;

wherein the optical head is configured and disposed such that the firstincident light beam and the receive axis form a triangulation planealong with the measurement point on the internally threaded surface, andwherein a line parallel to a tangent of the cylindrical cross-sectionwithin the triangulation plane is substantially perpendicular to boththe measurement axis and the central axis; and

wherein the apparatus is configured to register to the internallythreaded surface by making physical contact with the object in aplurality of contact locations, including at least two longitudinallyspaced contact locations on the internally threaded surface.

In another aspect, a method of measuring a profile of an internallythreaded surface using the apparatus described above is provided. In oneembodiment, the method includes the steps of:

-   -   (a) positioning the optical head on the measurement axis;    -   (b) moving the optical head on the measurement axis adjacent the        internally threaded surface;    -   (c) irradiating a plurality of measurement points along the        internally threaded surface using the first light source; and    -   (d) detecting scatter light generated at the plurality of        measurement points by the first light source to provide a        plurality of detector signal measurements; and    -   (e) determining a plurality of distance measurements, each        indicative of the distance from the optical head to a        measurement point, using the plurality of detector signal        measurements.

In another aspect, an apparatus configured to measure at least onephysical characteristic of a threaded surface of an object is provided.The threaded surface includes a central axis of the object defined by aplurality of crests of the threaded surface in the longitudinaldirection of the internally threaded surface, wherein the threadedsurface has a cylindrical latitudinal cross-section. In one embodiment,the apparatus includes:

-   -   (1) at least one motion stage configured to controllably move an        optical head along a measurement axis of the threaded surface,        wherein the measurement axis is defined by a plurality of crests        of the threaded surface in the longitudinal direction of the        threaded surface and the central axis lie in a common plane; and    -   (2) the optical head, comprising:    -   (i) an emission optical element in optical communication with a        first light source configured to emit a first incident light        beam onto the threaded surface to generate scattered light off        of the threaded surface at a measurement point;    -   (ii) a detector optical element in optical communication with a        first detector configured to receive at least a portion of the        scattered light from the measurement point, wherein the detector        optical element has a receive axis defined by the measurement        point, the detector optical element, and the first detector, and        wherein the first detector is configured to output a detector        signal indicative of the intensity and position of the scattered        light on the detector;

wherein the optical head is configured and disposed such that the firstincident light beam and the receive axis form a triangulation planealong with the measurement point on the threaded surface, and wherein aline parallel to a tangent of the cylindrical cross-section within thetriangulation plane is substantially perpendicular to both themeasurement axis and the central axis; and

wherein the apparatus is configured to register to the threaded surfaceby making physical contact with the object in a plurality of contactlocations, including at least two longitudinally spaced contactlocations on the threaded surface.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same become betterunderstood by reference to the following detailed description, whentaken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a perspective view of an embodiment of the thread profilerapparatus in accordance with aspects of the present disclosure;

FIG. 2 is a perspective view of an embodiment of the thread profilerapparatus in accordance with aspects of the present disclosure;

FIG. 3 is a side elevation view of an embodiment of the thread profilerapparatus in accordance with aspects of the present disclosure;

FIG. 4 is a partial cut-away side elevation view of an embodiment of thethread profiler apparatus in accordance with aspects of the presentdisclosure;

FIG. 5 is illustrates a representative use of an embodiment of thethread profiler apparatus to measure an internally threaded pipe, inaccordance with aspects of the present disclosure;

FIG. 6 is a partial cut-away view of an embodiment of the threadprofiler apparatus in accordance with aspects of the present disclosureshown measuring a threaded surface;

FIG. 7 is a diagrammatic representation of principles of opticaltriangulation as performed by embodiments of the thread profilerapparatus in accordance with aspects of the present disclosure;

FIGS. 8A and 8B are views down the central axis (8A) and on longitudinalcross-section (8B) of an object having an internally threaded surface inrelation to components of the thread profiler apparatus in accordancewith aspects of the present disclosure;

FIGS. 9A and 9B are views down the central axis (9A) and on longitudinalcross-section (9B) of an object having an internally threaded surface inrelation to components of the thread profiler apparatus in accordancewith aspects of the present disclosure;

FIG. 10 is a screen shot of a thread profile generated on a computerscreen using data generated by a thread profiler in accordance withaspects of the present disclosure;

FIGS. 11-13 are representative thread profiles measured by the threadprofiler and compared to the theoretical ideal profiles, in accordancewith aspects of the present disclosure;

FIGS. 14A and 14B are diagrammatic illustrations of an object having aninternally threaded surface in relation to components of the threadprofiler apparatus in accordance with aspects of the present disclosure;

FIG. 15 is an illustration of Reporubber® used to characterize a threadprofile; and

FIG. 16 is a stylus thread profiler.

DETAILED DESCRIPTION

An apparatus configured to measure at least one physical characteristicof a threaded surface of an object is provided. The apparatus usesoptical triangulation to perform non-contact characterization of thethreaded surface. The apparatus can be used to characterize variousaspects of the threaded surface, including generating the measurementsrequired to produce a longitudinal cross-sectional profile of thethreaded surface (referred to herein as a “thread profile”). Relatedly,the apparatus may be referred to herein as a “thread profiler.”

The threaded surface can be any surface having a cylindrical or conicalprofile and a helical thread. Internally threaded pipes are exemplaryobjects that can be characterized using the profiler. The threadedsurface includes a central axis of the object defined in thelongitudinal direction of the threaded surface, and a cylindricallatitudinal cross-section.

The threaded surface can be a thread having a profile selected from thegroup consisting of screw threads, pipe threads, ACME threads, buttressthreads, American Petroleum Institute threads, premium threads, andultra-premium threads. However, any thread profile can be measured,beyond those listed herein.

A thread profiler 100 in accordance with aspects of the presentdisclosure will now be described with reference to FIGS. 1-4. The threadprofiler 100 includes a motion stage 110 (e.g., a linear actuator) thatpositions an optical head 115 longitudinally along a measurement axis.The optical head 115 includes various optical components (e.g., lenses,optical fiber, a lights source, and/or a detector) for performing theoptical triangulation measurements required to generate a thread profileof an internally threaded surface. The optical head 115 is in mechanicaland electrical communication with a control unit 112, which may containoptical components (e.g., a lights source and/or a detector), parts ofan actuator, and/or electronic components (e.g., control electronics forthe optical components, computational components for processing datafrom the optical triangulation, and/or an actuator for the optical head115).

In certain embodiments, the optical head 115 includes:

-   -   (i) an emission optical element in optical communication with a        first light source configured to emit a first incident light        beam onto the internally threaded surface to generate scattered        light off of the internally threaded surface at a measurement        point; and    -   (ii) a detector optical element in optical communication with a        first detector configured to receive at least a portion of the        scattered light from the measurement point, wherein the detector        optical element has a receive axis defined by the measurement        point, the detector optical element, and the first detector, and        wherein the first detector is configured to output a detector        signal indicative of the intensity and position of the scattered        light on the detector; wherein the optical head is configured        and disposed such that the first incident light beam and the        receive axis form a triangulation plane along with the        measurement point on the internally threaded surface.

In certain embodiments, a line parallel to a tangent of the cylindricalcross-section within the triangulation plane is substantiallyperpendicular to both the measurement axis and the central axis.

The optical head 115 of the profiler 100 performs the basic distancemeasurement between the threaded surface and the optical head 115 as itpasses over the threaded surface along the measurement axis. The opticalhead includes an emission optical element, which is intermediate a lightsource and the measurement point. The emission optical element may beone or more of a fiber, mirror, lens, prism, or the like, as needed toproperly guide the first incident light beam from the light source tothe measurement point on the internally threaded surface. Similarly, theoptical head includes a detector optical element that can be a fiber,mirror, lens, prism, or the like, as needed to properly guide thescattered light to the first detector.

For example, if desired, the optical assembly may include afiber-coupled infrared (or other wavelength) laser source having a lensmounted on the end of the fiber so that the light will be focused to aspot at approximately mid-point in the measuring range. The optical head115 also may include a receive lens set that is used to project an imageof the light scattered from the laser source at the measurement point ona photo detector (e.g., a charge-coupled device (CCD), one-dimensionalcomplementary-metal-oxide-semiconductor (CMOS) array, or other pixelizedphoto detector). The optical head 115 may be calibrated as a unit on aseparate fixture before it is installed. The separate fixture may be acalibration fixture that the system would measure to perform thecalibration. Calibration of the optical assembly is typically necessaryin this example because there is a non-linear (but repeatable)relationship between the detector response and the radial distancemeasured to the measurement point.

The thread profiler 100 may use a fiber-coupled laser source to minimizethe physical size of the inspection head, such as for use in measuringsmall threads and small bore items. The fiber size may be chosen toachieve single-mode laser operation to minimize beam size andmeasurement errors due to any mode-hopping and allow focusing and beamsteering by the fiber. Miniature optical elements, such as prisms andlenses, may be integrated on the end of the fiber for focusing and beamredirection. For measuring larger threads and use with items havinglarger bore diameters, the thread profiler may include a laser sourceand collimating lens system without the use of fibers. Some form offolded optics (such as mirrors), may be required to achieve a compactassembly while maintaining the necessary source and receiver opticalpaths.

The power of the laser may be controlled to allow proper exposure ondifferent parts of the thread, as well as for different surfacefinishes. In certain embodiments, the proper exposure is based on themaximum received light level from previous samples. For example, ifmultiple reflections of the light are detected, and if the secondreflection is larger in amplitude than the first reflection, othermethods may be used, such as to analyze the entire detector response,select the correct reflection and then calculate the correct exposure.The detector location of the correct reflection can be estimated basedon the approximate known thread geometry.

In one embodiment, at least one of the first light source and the firstdetector are distant from the optical head 115, such that when theapparatus 100 is used to measure the internally threaded surface, firstlight source and the first detector do not enter the object.

In order to generate the most accurate thread profile, the optical head115 must travel on a measurement axis that is parallel to a line drawnthrough the thread crests of the internally threaded surface (see FIG.8B, “Measurement Axis”). The measurement axis may be in the same planeas the central axis (see FIG. 8B) of the object, as is the case withcylindrical threads, or the measurement axis may be angled with respectto the central axis, as is the case with tapered threads. In oneembodiment, the measurement axis is substantially parallel (i.e., 5degrees or less) to a taper angle of the internally threaded surface,such that the measurement axis and the central axis are not parallel.

So as to ensure that the optical head 115 travels on the propermeasurement axis, the profiler 100 includes a support 120 that is anelongated member extending longitudinally away from the profiler in thedirection of the measurement axis. The support 120 is disposed below theoptical head 115 and is parallel to the measurement axis on which theoptical head 115 extends.

The support 120 is configured to register the position of the apparatus100 to the internally threaded surface by making physical contact withthe object in a plurality of contact locations, including at least twolongitudinally spaced contact locations on the internally threadedsurface. By registering the position of the apparatus 100 to theinternally threaded surface, the taper angle of a thread is accountedfor and the measurement axis is adjusted accordingly.

In the embodiments illustrated in FIG. 1-4, the plurality of contactlocations include two distal contact surfaces 122, two proximal contactsurface 124, and two external contacts 130. The contact surfaces 122 and124 are configured to contact the internally threaded surface.Accordingly, they are elongated in the direction of the measurement axisso as to ensure that each contact surface 122 and 124 rests on at leastone thread crest.

It will be appreciated that balls or other contact surface forms canalso be used. However, if balls or other forms are used, steps must betaken to ensure that the contact surfaces each contact the thread crestin the same manner. For example, if balls are used, each ball must bedisposed such that it touches a thread crest or sits in the threadgroove, so as to not skew the measurement angle.

The contact surfaces 122 and 124 illustrated in the embodiments of FIG.1-4 are paired, such that there are two distal contact surfaces 122 andtwo proximal contact surfaces 124. However, the profiler 100 canincorporate the contact surface 122 and 124 in a number of combinations,including: two distal contact surfaces 122 and one proximal contactsurface 124 or two proximal contact surfaces 124 and one distal contactsurface 122. Therefore, in one embodiment, the apparatus is configuredto make physical contact with the internally threaded surface at twocontact locations distal to the apparatus and one contact locationproximal to the apparatus. In one embodiment, the apparatus isconfigured to make physical contact with the internally threaded surfaceat two contact locations proximal to the apparatus and one contactlocation distal to the apparatus. In one embodiment, the apparatus isconfigured to make physical contact with the internally threaded surfaceat two contact locations distal to the apparatus and two contactlocations proximal to the apparatus. In one embodiment, the apparatus isconfigured to make physical contact at two contact locations on anexterior surface of the object, wherein the exterior surface isperpendicular to the central axis of the internally threaded surface. Inone embodiment, the apparatus further comprises a plurality of contactsurfaces, each extending parallel to the measurement axis, and whereinthe plurality of contact surfaces are configured to provide theplurality of contact locations on the internally threaded surface.

In the illustrated embodiment, the external contacts 130 are shaped aspaddles perpendicular to the internally threaded surface, so as tocontact the face of the object, which is typically the reference surfaceused for forming an internal thread. However, the embodiments of theprofiler 100 are not limited to use on threads having a faceperpendicular to the internally threaded surface. Additionally, theexternal contacts 130 need not be paddles, as illustrated, but can be ofany shape and configuration that provides the necessary registration ofthe profiler to the correct measurement axis.

The configuration of the contact surfaces 122 and 124 required toproperly register the profiler 100 on the measurement axis relates towhether or not external contacts 130 are used. For American PetroleumInstitute (API) style threads, the front face of the object (e.g., pipe)provides a convenient reference location to establish the measurementaxis in the same plane as the central axis. This requires a minimum oftwo points on the front face. Also, because the front face is arelatively large area, the two points can be sufficiently separated suchthat it provides a high degree of accuracy and repeatability. All threadprofile geometry is based on slicing the thread through the centralaxis.

The second reference requirement is to position the measurement axissuch that it is substantially parallel to the thread inner surface.There are two reasons for this. First, this minimizes the requiredmeasuring range of the optical triangulation sensor. Second, it assuresthat the angle between the triangulation plane and the thread flanks isconsistent. This is particularly important when this angle is acute.This second reference is established by at least one contact point eachat the distal and proximal ends of the thread profiler (i.e., via thesupport).

The third reference establishes the angular position of the light source(and associated receive axis) relative to the plane established by thecentral and measurement axis. This reference is established by using twocontact points separated in the latitudinal direction. The two contactpoints can be located either at the distal or proximal end of the threadprofiler. This provides a minimum of 3 contact points on the innerthread surface that serve to provide the second and third referencerequirements. Two latitudinally separated reference points on the innersurface can also provide the first reference to keep the measurementaxis and central axis in the same plane; however it will not be asaccurate. For threads without an accurately machined front fact, thiswill be the only method of alignment. The accuracy required will dependon the size of the thread, the larger the thread, the less the axisalignment requirement.

In one embodiment, the plurality contact locations are contactedsimultaneously to the threaded surface in order to register the positionof the apparatus in relation to the internally threaded surface. Such anembodiment is illustrated in FIGS. 1-5, wherein the contact surfaces 122and 124, and external contacts 130 all contact the object. In otherembodiments, however, the plurality of contact locations are contactedseparately, such as in a robotic system wherein the contact locationsare contacted as reference points to define the measurement axis onwhich the robotic system should move the optical head.

The motion stage 110 is useful to translate the optical head 115 alongthe measurement axis as data is collected and stored. Ideally, thismotion is smooth and at a reasonably consistent velocity—the consistencyof which depends on how well the measurement instant is synchronizedwith the axis position information as well as the variation in geometryof the threaded surface—such that the optical assembly moves in astraight line with minimal Abbe errors. The motion stage 110 may includea linear bearing to assure smooth motion, an encoder to synchronize thedata collection with the stage position, and/or a passive drivemechanism to actuate the motion. If used, an encoder providessynchronized position output versus the laser-measured thread height toaccurately determine thread profile. A finger actuated trigger may beincluded to initiate the inspection motion.

The thread profiler 100 requires smooth vibration-free motion as itscans the surface of the threads. This may be obtained by using a firmconnection between the thread profiler and the item to be inspected,such as described above. Ideally, the tool also should minimize internalvibrations during the measurement process. For example, an electricmotor and drive mechanism may be included, but would increase complexityand cost and add moving parts. As another example, a hydraulicallydampened spring driven device using a single compression spring or dualcompression springs to attempt to achieve a linear motion velocity maybe used.

Constant velocity is useful because it maintains a consistent number ofheight measurements per unit distance traveled. Although the heightmeasurements are collected at known longitudinal axial distances withinthe item to be measured by using an encoder, the spacing between thesamples may become too large if the optical head 115 is moving too fast.For example, the mechanism used to drive the optical head 115 mayinclude an Airpot unit, which dampens the driving force supplied byconstant force springs. Providing a uniform velocity for the opticalhead 115 is believed to achieve the uniform sampling requirement. TheAirpot unit may, for example, include one or more springs and acommercially available air cylinder device having a precisely matchedpiston sliding over a polished bore to assure smooth vibration-freemotion of the piston and not require any electrical power.

A uniform velocity also reduces height measurement offsets whenmeasuring on the flanks. Ideally, the encoder position should be read atthe middle of the measurement exposure to eliminate this source oferror. In certain embodiments, thread profiler 100 uses a short lightexposure time, as well as a slow velocity, to minimize this errorsource. If the exposure or velocity increases, this effect must bemitigated, such as by synchronization of the exposure/light source withthe encoder.

In the illustrated embodiment of FIG. 1-4, the profiler 100 isconfigured to secure to the object having the internally threadedsurface. While any securing mechanism known to those of skill in the artcan be used, including magnets and suction, a releasable clamp 135 isused in the illustrated embodiment. The clamp 135 can be tightened on anexterior surface of the object, so as to position the support 120 on theinternally threaded surface. As an example, FIG. 5 illustrates theprofiler 100 immobilized against an internally threaded pipe 200 usingthe clamp 135. The profiler 100 is positioned in relation to the threadsof the pipe 200 by the support 120, which in turn positions the opticalhead 115 such that it can be extended above the internal threads inorder characterize the internally threaded surface (e.g., to generate athread profile).

In the embodiment illustrated in FIGS. 1-5, the clamp 135 includes ahand-operated knob, such as on the bottom of the profiler 100, which maybe tightened to assure a firm contact between the thread profiler 100and the item to be inspected. The thread profiler may include areference contact point to be held snug against the face of the item tobe inspected. In this example, the face of the item serves as theperpendicular reference for the axis of the thread. The thread profilermay include one or more engaging teeth to assist in pulling ormaintaining the thread profiler against the reference face of the itemto be inspected.

In one embodiment, the apparatus includes at least one magnet configuredto secure the object to the apparatus and to register the apparatus in aposition in relation to the object.

In one embodiment, the apparatus is portable. The embodiment illustratedin FIGS. 1-5 is sized and configured to be hand-held and portable, suchthat the profiler 100 can be brought to the object, as opposed to theprofiler 100 being fixed in space and bringing the object to theprofiler 100. Accordingly, the profiler 100 includes all of thenecessary components to generate a thread profile while being held inthe user's hand.

The optical head 115 is shown in cut-away in FIG. 4, so as to illustratethat the optical head 115 includes an opening 140, through which both alight emission signal and a receive axis for light detection pass. Acavity 145 allows for the arrangement of optical elements for emissionand/or detection to be arranged. These components may include lenses,mirrors, filters, optical fibers, and the like. A light source and/or adetector may also be packaged into the optical head 115/cavity 145,although such components are typically too large to fit into the opticalhead 115. Accordingly, in certain embodiments, the light source anddetector are contained within the body of the profiler 100 and do notextend into the object with the optical head 115.

FIG. 6 illustrates a representative emission/detection system, such ascan be used with the optical head 115 in FIGS. 1-5. The system includesa laser as the light source, which is coupled to an optical fiber fortransmission of light to the distal end of the optical head, where it isemitted through the beam-forming optics (e.g., a lens or prism). Thelight is emitted onto a measurement point on the internal thread, whichgenerates scattered light. The scattered light is captured by a mirrorthat directs through an imaging lens onto a point (“spot”) on a CCDarray detector. According to the principles of optical triangulation,the position of the imaged spot on the detector varies as the distancebetween the surface of the internal thread and the optical head changes,as will be described in more detail below. While specific components(e.g., laser, CCD, fiber, mirror, lens, etc.) are disclosed in thisembodiment, it will be appreciated that any components can be used aslong as optical triangulation is facilitated so as to measure thedistance between the optical head and the internally threaded surface.For example, a light-emitting diode can be used instead of a laserand/or any pixilated photo detector can be used instead of the CCDdetector, etc.

The thread profiler apparatus and methods of the present disclosureutilize optical triangulation. Optical triangulation is a geometricapproach to measuring distance, where a focused beam of light isprojected onto the surface to be measured and the reflected light isimaged onto a position-sensitive photo detector.

Referring to the exemplary embodiment of FIG. 7, components of anexemplary thread profiler in accordance with the present disclosureincludes a laser light source, an imaging lens as an optical element,and position-sensitive photo detector. As described herein, thesecomponents may be housed together in a single apparatus or a singleoptical probe. The optical probe housing may provide a fixed and stablegeometry between the components. The photo detector may, in someapplications, be a one-dimension pixelized detector, similar to thetwo-dimensional detectors used in cameras.

The angle between the light projection axis (“laser beam”) and thereceive axis of the imaging lens allows for measurement of the positionof the measurement point in relation to the optical head. The receiveaxis extends between the focused spot of light at the measurement pointon the thread surface and the center of the imaging lens. Changing thedistance between the optical head and the thread surface pivots thereceive axis slightly about the imaging lens, which in turn causes theposition of the imaged spot on the position-sensitive photo detector tochange location. A larger average angle between the projection andreceive axis causes a larger position change on the position sensitivephoto detector. This angle may be selected depending upon the particulardesign. For example, this angle may be in the range of 20 to 45 degreesin some applications.

In the first representative measurement geometry, as shown in FIGS. 8Aand 8B, the optical triangulation plane is substantially perpendicular(i.e., within the helix angle of the thread) to the thread axis. Theoptical triangulation plane is the plane created by the light source(“laser”) beam and the receive axis (e.g., the center of the receivelens. The triangulation plane is substantially perpendicular to themeasurement axis in one plane, while the other plane stays perpendicularto the central axis. This geometry is referred to herein as the“perpendicular geometry” because the triangulation plane issubstantially perpendicular to the measurement axis.

In the second representative measurement geometry (the “parallelgeometry”), the triangulation plane is parallel to the axis of thethread, but will require two receive axes fore and aft of the lasersource, as illustrated in FIGS. 9A and 9B. A fore sensor is used for oneflank of the thread and an aft sensor is used for the other flank as theoptical head traverses the thread. Accurate results may be difficult toobtain if the optical receive axis is shallow with respect to the flanksurface; therefore the receive path having an axis closest to aperpendicular angle with respect to the flank is preferred for aspecific flank. This approach typically requires a smaller triangulationangle to reach the roots of the thread (compared to the perpendiculargeometry), increasing the measurement noise due to surface reflectivityvariations. This particular geometry suffers from added complexity, suchas in the additional number of components and the need to collectprofile data from two different sensors. However, this geometry providestwice as much data in the roots and crests of the thread because bothsensors will see the crests, because neither is shadowed; thereforetwice as much data will be collected.

Still with reference to use of the exemplary embodiments, it may, insome applications, be useful to have the laser source perpendicular tothe surface tangent plane for measurement purposes. If the laser is notperpendicular to the surface, the point on the surface where the laserbeam of this embodiment strikes the surface moves circumferentiallyaround the thread as the radius of the thread changes. Thisconsideration may be more important for smaller diameter threads becauseof the tight radius of curvature.

In an example operation of the illustrated thread profiler, processingof data from the sensor(s) requires first reflection (of light off thethread surface) to be analyzed. This is the reflection that representsthe smallest radii, which is important when the parallel measurementgeometry is used, as the secondary reflection from the opposing flank iswithin the field of view of the detector(s). The laser light willreflect off of the first flank, reflect further down into the threadroot and then reflect off of the opposing flank. The perpendicularmeasurement geometry may have a similar problem if there is debris inthe thread root and depending on the reflectance distribution of thethread surface and the debris surface.

In certain embodiments, the detected signal is processed so as toidentify the first reflection from several reflection signals. In ahighly-reflective environment or for certain thread shapes and surfacefinish, the first reflection may not be the highest intensity peak atthe detector. In such a situation, all reflections are identified andbecause the overall thread geometry is approximately known (the operatorwill know what type of thread that is being inspected) the spuriouspeaks can be eliminated because they will deviate significantly fromoverall thread form. This method can also be used in situation where thefirst reflection is not the correct location or if the correct locationdoes not provide a detectable reflection on the detector.

In certain embodiments, a line parallel to a tangent of the cylindricalcross-section within the triangulation plane is substantiallyperpendicular to both the measurement axis and the central axis. Inorder to clarify the spatial organization of the profiler, FIGS. 14A and14B illustrate representative embodiments of components of a profilerarranged in relation to an internally threaded surface.

FIGS. 14A and 14B illustrate the preferred measurement geometry. Theoptical triangulation plane is defined by the laser axis, receive axisand the measurement point. The central axis of the thread and themeasurement axis both lie in the same plane such that the plane cuts ina radial direction through the threads. The line tangent to the cylinderis shown at the thread surface and is perpendicular to the measurementaxis. The triangulation plane is oriented such that when projected willsubstantially include the tangent line within normal helix anglevariations. FIG. 14A illustrates the optical triangulation plane insubstantially the same plane as a latitudinal cross-section of theobject. In order to measure steep thread flank angles, the opticaltriangulation plane may be tilted aft or fore, as illustrated in FIG.14B.

In certain embodiments, the apparatus is configured to interface with acomputer, or includes a computer configured to transform the detectorsignal into a measurement of the distance from the optical head to themeasurement point using the optical triangulation geometry, as known tothose of skill in the art.

A standard personal computer (PC) compatible computer is used inconnection with this embodiment to collect, process, and store the data.In this example, a Universal Serial Bus (USB) cable is used to power thedevice through the PC compatible laptop computer. However, it will beappreciated that all of the computing functions can be contained withinthe body of the profiler 100. For example, an embedded computer with aUSB interface can be used to coordinate the data collection, preprocessthe data from the detector, control the laser and format the data fortransfer to a separate computer.

Exemplary output data of a measure thread profile is shown in FIG. 10.From such a data set, various aspects of the measure thread can bedetermined, including items such as the root to crest distance,machining imperfections or wear that cause malformed or rounded flanksand crests, thread pitch, deviations in the taper, and flank angle.

FIGS. 11-13 are exemplary thread profiles obtained by measuring thereferenced threads across a distance of 1.000″. The thread forms includeround coupling threads (FIG. 11); API thread (FIG. 12); and a full holeAPI thread (FIG. 13). Dashed lines are included as the theoretical idealprofile, which is typically indistinguishable from the measured profile,thereby illustrating the accuracy and precision of the profiler.

The exemplary embodiment is designed so that the PC can output a scaleddigital file (currently in the industry standard.dxf file format) thatcan be printed and used to overlay with a theoretical profile of thethread shape to allow the inspector to determine if the profile meetsmanufacturing or refurbishment requirements. Alternatively, thiscomparison can be made automatically by the software, such as if theaccept/reject criteria is encoded in the software. This “theoreticalprofile” information can be stored in the device using a database orsimilar scheme so that information can be easily stored and retrievedfrom the database for automatic comparison. In addition, the softwarecan automatically highlight areas of concern on the profile and displaythe overlay to the operator. If desired, the database information can beencrypted, such as to protect the information from competitors, whilestill providing the comparison feature by not displaying the overalldimension and only highlighting and quantifying differences.

The thread profiler may have any suitable power supply and communicationand display arrangements. In some embodiments, the thread profiler maybe battery powered with wireless communications to the PC. In otherembodiments, the thread profiler may include a USB connection betweenthe thread profiler and the PC for providing power and communicationscapabilities. The thread profiler may include a display guiding theoperation, with results displayed on the PC located near to the threadprofiler. For another example, the thread profiler may bebattery-powered or powered from an external source with built-inprocessing capabilities and built-in results display feature(s) ranging,for example, from a go/no go display to a full up zoomable resultsdisplay. If desired, the detailed measurements can be queued into thedevice and later downloaded to a PC for storage or further analysis asneeded. In some embodiments, the thread profiler can be “wi-fi”configured, such as to allow statistical process control (SPC) data tobe tracked quickly or easily tied in with a manufacturing operation.

In one embodiment, the apparatus is configured to measure a plurality ofmeasurement points along the measurement axis and the computer isconfigured to generate a radial cross-sectional profile (a “measuredprofile”) of the internally threaded surface along the measurement axisusing the measurements of the plurality of measurement points.

In one embodiment, the computer is configured to compare the radialcross-sectional profile to an ideal profile in order to determinedeviations between the profiles. By comparing an ideal profile to themeasured profile allows defects to the shape of the threads to bedetermined. Such defects include items such as the root to crestdistance, machining imperfections or wear that cause malformed orrounded flanks and crests, thread pitch, deviations in the taper, and/orflank angle.

In certain embodiments, the thread profiler includes built-inself-calibration features for a minimum of one or more heights and abuilt-in mechanical “dead zone” on mechanism travel (similar to a camerashutter delay) to ensure vibrations due to handling will dampen beforedata is collected. For example, this may allow time for the operator tomanually initiate the scan and remove his/her hand before the motionstarts.

In one embodiment, the optical head is configured such that thetriangulation plane rotated about the line parallel to the tangent ofthe cylindrical cross-section within the triangulation plane that issubstantially perpendicular to both the measurement axis and the centralaxis, within normal variations of the helix angle. This changes the“look” angle to allow acute or negative flank angles to be measured.This typically would require two optical heads to be used, one for theleading flank and one for the trailing flank. The “look” angle may bedifferent depending of the leading and trailing flank angles.Accordingly, in certain embodiments, a second light source and a seconddetector, paired together, are incorporated into the apparatus.

In one embodiment, the apparatus is configured to adjust a parameterselected from the group consisting of light source power, light sourcepulse width, detector exposure time, and combinations thereof. Theamount of light scattered from the surface of the thread can varysignificantly depending on the surface finish and relative anglesbetween the laser, receive axis and thread surface. This often willrequire a combination two or three of the above items. In oneembodiment, the light source power is continuously adjusted as themeasurements are collected, while the detector exposure can be modifiedbetween measurement to accommodate newly manufactured threads ascompared to used threads. There also maybe variations in the detectedlight levels due to the geometry of specific thread types.

In one embodiment, the apparatus is capable of measuring threads havinga thread flank angle of from 45 to −10 degrees, as measured from a lineperpendicular to the taper angle.

In another aspect, a method of measuring a profile of an internallythreaded surface using the apparatus of claim 1 is provided. In oneembodiment, the method includes the steps of:

-   -   (a) positioning the optical head on the measurement axis;    -   (b) moving the optical head on the measurement axis adjacent the        internally threaded surface;    -   (c) irradiating a plurality of measurement points along the        internally threaded surface using the first light source; and    -   (d) detecting scatter light generated at the plurality of        measurement points by the first light source to provide a        plurality of detector signal measurements; and    -   (e) determining a plurality of distance measurements, each        indicative of the distance from the optical head to a        measurement point, using the plurality of detector signal        measurements.

An exemplary operational procedure for measuring a thread profileincludes:

The operational sequence of the tool is as follows:

-   -   1. Select the depth within the thread where the profile data        will be collected. For example, the tool can begin collection at        1.5, 2.5 or 3.5 inches from the face of the pipe end. This can        be accomplished by physically adjusting the position of the        motion stage in relation to where the profiler contacts the pipe        end.    -   2. Insert the profiler into the internally thread part until the        front reference paddles evenly contact the face of the pipe. It        is important both paddles are flush with the face of the pipe to        keep the measurement axis in the same plane as the central        thread axis.    -   3. Rotate the knob below the unit until the reference surface        contacts the outside of the internally threaded pipe. This        clamps the profiler to the part and ensures there is no relative        motion between the pipe and the profiler during the measurement.    -   4. Pull the knob at the base of the handle to retract the        mechanism to the scan start location.    -   5. Prepare the interfaced computer to receive data from the        profiler.    -   6. Squeeze the trigger on the profiler to begin the measurement        cycle. The radial data is displayed in real-time on the screen        over the one inch axial length of travel.    -   7. Once the data is collected, the software can automatically        overlay the theoretical profile on the data collected.        Variations can be noted by the software.

In one embodiment, moving the optical head is synchronized withirradiating the plurality of measurement points, so as to coordinate theplurality of distance measurement with a specific position of theoptical head on the measurement axis for each of the plurality ofmeasurement points.

In one embodiment, moving the optical head is synchronized withdetecting the scattered light from the plurality of measurement points,so as to coordinate the plurality of distance measurements with aspecific position of the optical head on the measurement axis for eachof the plurality of measurement points. Such coordination allows, forexample, the measurements to be taken at consistent positions fromthread to thread (e.g., the same number of data points on each flank,crest, and root.

In one embodiment, moving the optical head comprises circular movementaround the circular latitudinal cross-section or the helix angle of theinternally threaded surface.

In one embodiment, the method further comprises the step of adjusting aparameter selected from the group consisting of light source power,light source pulse width, detector exposure time, and combinationsthereof.

In one embodiment, the method further comprises the step of generating aprofile of the internally threaded surface from the plurality ofdistance measurements.

In one embodiment, the method further comprises the step of comparingthe generated profile to an ideal profile.

While the above described embodiments are used for characterizing (e.g.,profiling) an internally threaded surface, embodiments of the presentdisclosure may be used in a thread profiler for characterizing externalthreads. For example, the mechanism used to clamp the device on thethread component can be modified to allow the optical measurement headto be positioned on the outside of the thread and to scan axially.

Accordingly, in another aspect, an apparatus configured to measure atleast one physical characteristic of a threaded surface of an object isprovided. The threaded surface includes a central axis of the objectdefined by a plurality of crests of the threaded surface in thelongitudinal direction of the internally threaded surface, wherein thethreaded surface has a cylindrical latitudinal cross-section. In oneembodiment, the apparatus includes:

-   -   (1) at least one motion stage configured to controllably move an        optical head along a measurement axis of the threaded surface,        wherein the measurement axis is defined by a plurality of crests        of the threaded surface in the longitudinal direction of the        threaded surface and the central axis lie in a common plane; and    -   (2) the optical head, comprising:    -   (i) an emission optical element in optical communication with a        first light source configured to emit a first incident light        beam onto the threaded surface to generate scattered light off        of the threaded surface at a measurement point;    -   (ii) a detector optical element in optical communication with a        first detector configured to receive at least a portion of the        scattered light from the measurement point, wherein the detector        optical element has a receive axis defined by the measurement        point, the detector optical element, and the first detector, and        wherein the first detector is configured to output a detector        signal indicative of the intensity and position of the scattered        light on the detector;

wherein the optical head is configured and disposed such that the firstincident light beam and the receive axis form a triangulation planealong with the measurement point on the threaded surface, and wherein aline parallel to a tangent of the cylindrical cross-section within thetriangulation plane is substantially perpendicular to both themeasurement axis and the central axis; and

wherein the apparatus is configured to register to the threaded surfaceby making physical contact with the object in a plurality of contactlocations, including at least two longitudinally spaced contactlocations on the threaded surface.

Embodiments of this aspect are similar to those set forth above anddescribed with reference to an internally threaded surface. The threadprofiler can be “reversed” and also used on an externally threadedsurface according to the same geometric constraints as when the profileris used on internal threads.

While illustrative embodiments have been illustrated and described, itwill be appreciated that various changes can be made therein withoutdeparting from the spirit and scope of the invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A method of measuring aprofile of a threaded surface of an object using an apparatus, themethod comprising the steps of: (a) registering, by the apparatus, thethreaded surface of the object to define a registration plane; (b)positioning an optical head of the apparatus on a measurement axis,wherein the measurement axis is substantially parallel to theregistration plane; (c) moving the optical head on the measurement axis;(d) irradiating, by the apparatus, a plurality of measurement pointsalong the threaded surface using a first light source of the apparatus;(e) detecting, by the apparatus, scattered light generated at theplurality of measurement points by the first light source to provide aplurality of detector signal measurements; (f) determining a pluralityof distance measurements, each indicative of the distance from theoptical head to a measurement point, using the plurality of detectorsignal measurements; and (g) comparing the plurality of distancemeasurements to a theoretical profile of the threaded surface.
 2. Themethod of claim 1, wherein comparing the plurality of distancemeasurements to a theoretical profile of the threaded surface furthercomprises rejecting one or more of the plurality of distancemeasurements as not meeting an accept/reject criteria.
 3. The method ofclaim 1, further comprising overlaying the theoretical profile with theplurality of distance measurements.
 4. The method of claim 1, whereinthe threaded surface comprises threads with a thread flank angle of from45 to −10 degrees.
 5. The method of claim 1, wherein the threadedsurface of the object is a tapered threaded surface of the object, andwherein the measurement axis is substantially parallel to a taper angleof the tapered threaded surface such that the measurement axis and acentral axis of the object are not parallel.
 6. The method of claim 1,wherein the measurement axis is substantially parallel to a thread axisof the threaded surface of the object.
 7. A thread measurement apparatusfor measuring at least one physical characteristic of a threaded surfaceof an object, the apparatus comprising: a body configured to register asurface of the object, wherein said registration defines a registrationplane; and at least one motion stage configured to controllably move anoptical head along a measurement axis that is substantially parallel tothe registration plane; wherein the optical head comprises: an emissionoptical element configured to emit a first incident light beam onto thethreaded surface at a measurement point to generate scattered light offof the threaded surface, and a detector configured to receive at least aportion of the scattered light and generate a detector signal related tothe measurement point; and a computer configured to transform thedetector signal into a measurement of the distance from the optical headto the measurement point and compare a plurality of measurements to atheoretical profile of the threaded surface.
 8. The thread measurementapparatus of claim 7, wherein the body comprises a support membercomprising a plurality of contact surfaces configured to register thesurface of the object to define the registration plane.
 9. The threadmeasurement apparatus of claim 7, wherein the body is configured toattach to a robotic system and to register the surface of the object bycontacting a plurality of contact locations separately as referencepoints to defines the registration plane.
 10. The thread measurementapparatus of claim 7, wherein the computer is within the body of thethread measurement apparatus.
 11. The thread measurement apparatus ofclaim 7, wherein the thread measurement apparatus is capable ofmeasuring threads having a thread flank angle of from 45 to −10 degrees.12. The thread measurement apparatus of claim 7, wherein the threadedsurface of the object is a tapered threaded surface of the object, andwherein the measurement axis is substantially parallel to a taper angleof the tapered threaded surface such that the measurement axis and acentral axis of the object are not parallel.
 13. The thread measurementapparatus of claim 7, wherein the measurement axis is substantiallyparallel to a thread axis of the threaded surface of the object.